(a) Technical Field of the Invention
The present invention relates to a constraint mechanism for a steering device of a four-wheeled vehicle, and in particularly to such a mechanism that allows easy modification or change of setting for maximum steering angle of front wheels of the vehicle.
(b) Description of the Prior Art
A four-wheeled vehicle is commonly provided with a steering device at a location associated with the driver seat. As shown in FIGS. 1 and 2, a conventional steering device, generally designated at 1, comprises a steering wheel 11, a steering column 12, a lower column 14, and a steering gear box 15. The steering wheel 11 is mounted to an upper end of the steering column 12 and the lower column 14 is coupled to a lower end of the steering column 12 via a universal joint 13. A lower end of the lower column 14 is coupled, via another universal joint 13, to a screw rod 152 of the steering gear box 15. The steering gear box 15 comprises a hollow housing 151 accommodating therein a rack 153 and the screw rod 152. Opposite ends of the rack 153 are respectively connected to steering tie rods 16, which are coupled to kingpins of front wheels of the four-wheeled vehicle. Thus, when the steering wheel 11 is rotated, the steering column 12 and the lower column 14 are rotated simultaneously. This causes the steering gear box 15 to move the tire rods 16 in a left-right direction and thus changes the angular orientation of the front wheels and in turn changing the moving direction of the vehicle.
The angular displacement or steering angle of the front wheels is subjected limitation or constraint imposed by the steering device 1 and this will be explained with particular reference to FIG. 2. Since the structures on the opposite sides of the steering gear box 15 are substantially the same, in the following description, reference is made only to the structure on one side (the left side) of the steering gear box 15. As shown in FIG. 2, when the screw rod 152 is rotated by the steering wheel 11, the engagement between the screw rod 152 and the rack 153 causes the rack 153 to synchronously move. Thus, the rack 153 and the tie rod 16 coupled thereto are moved in the left-right direction to change the angular position or steering angle of the front wheel with respect to a moving direction of the vehicle. A spherical joint 161 that couples the tie rod 16 to the rack 153 comprises an anti-loosening washer 162, which, when the rack 153 and the tie rod 16 are moved to a limit position, is brought into contact with a distal free end 1511 of the housing 151. This defines the limit position, corresponding to the maximum steering angle of the front wheel with respect to the vehicle.
The conventional steering device 1, although effective in ensuring proper steering of the front wheels of the vehicle, suffers the following disadvantages:
(1) Since the anti-loosening washer 162 of the spherical joint 161 of the tie rod 16 frequently hits the front end 151 of the housing 151 due to the steering operation and since the housing 151 is commonly made of aluminum based alloys that are of low hardness, the front edge 1511 of the housing 151 of the steering gear box 151 is often subjected to undesired deformation or even being broken, and consequently, replacement of the gear box 151 must be done for repairing purposes.
(2) In case that the design or manufacturing of vehicle is changed and there is a need to set new limitation to the steering angle of the front wheels of the vehicle, a new mold is needed for molding new design housing 151 of the new gear box 15 so that a proper length of the housing 151 is provided to effect the desired new steering configuration. This certainly increases the overall costs of the steering gear box 15.
Thus, in view of the above-discussed drawbacks of conventional four-wheeled vehicle, the present invention is aimed to overcome the problems associated with the engineering change caused by the desire of modification of steering device to cope with different angular limitation of steering and the problems associated with the unacceptable durability of the conventional steering gear box 15 caused by the anti-loosening washer 162 of the spherical joint 161 of the tie rod 16 frequently hitting the free end 1511 of the housing 15 of the gear box 15.